Structural evolution of in situ boron-doped SiGe ultrathin film analyzed by multi-optical methods

Abstract

In situ boron (B)-doped SiGe (BSG) layer is extensively used in the source (S)/(D) drain of metal-oxide-semiconductor field-effect transistors. An unexpected structural evolution occurs in BSG during metallization and activation annealing during actual fabrication, which involves a correlated interaction between B and SiGe. Herein, the complicated phenomena of the structural evolution of BSG were analyzed by 325 nm micro-Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), reflective second harmonic generation (RSHG), and synchrotron x-ray diffraction (XRD). Optical inspection was integrated into these processes to establish a multi-optical method. 325 nm micro-Raman spectroscopy was used to determine variations in Si–Si, Si–Ge, and Ge–Ge bonds in BSG. XPS exhibited the binding energy evolution of Ge3d during different annealing processes at varied Ge ratios and B concentrations. RSHG revealed the polar Si-B and Ge-B bonds formed during annealing. Synchrotron XRD provided the structure and strain changes of BSG. Secondary-ion mass spectrometer profiles provided the species distribution, which was used to examine the results of multi-optical method. Furthermore, double-layered BSG (DBSG) with different B concentrations were analyzed using the multi-optical method. Results revealed that Ge aggregated in the homogeneous interface of DBSG, and that B dopants in BSG served as carrier providers that strongly influenced the BSG structure. However, BSG with excessive B concentration was unstable and increased the B content (SiB3) through metallization. For BSG with a suitable B concentration, the formation of Si–B and Ge–B bonds suppressed the diffusion of Ge from SiGe, thereby reducing the possibility of Ge loss and further B pipe-up in the heavily doped S/D region.